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Amplified Parts
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|-+  British Style
| |-+  JTM 45, 50
| | |-+  bias question
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Author Topic: bias question  (Read 3993 times)
jerrydyer
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« on: June 20, 2008, 03:49:48 PM »

I have a JTM45 ceriatone on the bench. looks like it was dropped. Installed new power tubes. bias ris runaway. goes up to about 62 watts each before I turn it off   should i replace the rectifier and try again? thanx
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bloodedge
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« Reply #1 on: June 21, 2008, 03:53:32 PM »

I had a problem with bias that go out of spect in past.
It happened to be a bad contact with powertube socket.

I didnt replace the socket, just tightened it a bit and i never had a problem with this again Smiley.
Trough it was happening in only 1 socket/powertube.

Am not a pro but here what iwould do.
I would check for voltage of the powertubes if you can(taking REALLY care of high voltage)
So you can know if the bias circuit supply the powertube correctly, etc.

Also, i think it is recommanded to change the rectifier tube when you change the powertubes so it can be this too.
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Roe
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« Reply #2 on: June 22, 2008, 04:57:30 PM »

adjust the bias. just change the bias resistor if the range is too high or low
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